The environment is everywhere.

Following up on plants that tweet when they need watering, the device is supposed to send out a tweet as a result of over-watering, as well! Over-watering is the second most common reason why house plants do not survive, after under-watering.

Once soil is saturated (that is, there are no more air spaces available for water), the sensors employed on such kits will not change their reading when water is added beyond that point. Therefore, this device presumably has a set point reflective of soil saturation, ensuring that water is added only to a point just below saturation, which probably is a good thing.